In a known digester apparatus, a plurality of centrally located concentric pipes are provided. An inner surface of the inner-most pipe defines a wash downcomer for providing a cold blow filtrate for cooling and washing pulp near the base of the digester apparatus. A cooking downcomer is defined by the outer surface of the inner-most pipe and the inner surface of a directly adjacent second-inner-most pipe. The cooking liquor flows through the cooking downcomer and exits near a mid-point of the digester apparatus. The temperature of the cold blow filtrate entering the wash downcomer may be from about 120° F. to about 160° F., while the temperature of the cooking liquor entering the cooking downcomer may be at a temperature of from about 285° F. to about 340° F. However, because the wash and cooking downcomers are directly adjacent to one another, undesirable heat transfer occurs between the two downcomers, which makes the overall process less efficient and effective.